Grinding machine

ABSTRACT

In a cylindrical grinding machine for grinding a rotating cylindrical workpiece with a rotating grinding wheel, a wheel spindle for supporting the grinding wheel is divided at its axial mid portion into first and second spindle components, and respective ends on the sides opposite to the axial mid portion of the first and second spindle components are rotatably supported by a pair of fluid bearings. Each of the first and second spindle components has at least at its portion supported by a corresponding one of the fluid bearings a diameter which is determined to secure a predetermined rigidity at a grinding point between the grinding wheel and the workpiece, based on a predetermined value obtained taking into consideration the power consumption by the fluid bearings or the quantity of energy consumption required from the beginning to the ending of a grinding operation. Thus, the grinding machine can be reduced in the energy consumed from the beginning to the ending of the grinding operation.

INCORPORATION BY REFERENCE

This application is based on and claims priority under 35 U.S.C. 119 with respect to Japanese Application No. 2004-371074 filed on Dec. 22, 2004, the entire content of which is incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a grinding machine for grinding a workpiece with a rotating grinding wheel, and in particular, it relates to an environment-oriented, energy-saving grinding machine capable of reducing the quantity of energy consumed from the beginning to the ending of a workpiece grinding.

2. Discussion of the Related Art

Heretofore, there has been known a grinding machine of the type that a wheel head on which a grinding wheel is supported by static pressure bearings in the form of a cantilever to be drivingly rotatable is mounted on a bed through a slide mechanism to be movable toward and away from a work head and a foot stock and that a workpiece which is supported between the work head and the foot stock to be drivingly rotatable is ground with the grinding wheel with coolant being showered thereon from a coolant nozzle, as described, for example, in Japanese unexamined, published patent application No. 10-118922 (hereafter referred to as Patent Document 1).

Patent Document 1 discloses a grinding machine which has a wheel head drivingly rotatably carrying a grinding wheel by static pressure bearings in the form of a cantilever and a wheel head feed mechanism for mounting the wheel head through a slide mechanism on a bed to be movable toward and away from a work head and a foot stock.

In the prior art grinding machine, there is taken a construction that the grinding wheel is drivingly rotatably carried by the static pressure bearings on the wheel head in the form of cantilever. Thus, a spindle for the grinding wheel and the diameter of bearing components have been designed to be large for the purpose of increasing the rigidity during the grinding operation thereby to keep the machining accuracy high.

However, in the prior art grinding machine, since the bearings for the grinding wheel are arranged to support the grinding wheel in the form of cantilever wherein the spindle for the grinding wheel and the diameter of the bearing components have to be designed to be large for the purpose of increasing the rigidity during the grinding operation thereby to keep the machining accuracy high, the friction force generated in each bearing is large, and hence, a large power is required for idle rotation of the spindle. With this, the quantity of heat generation at each bearing is large, and a bearing oil cooler for cooling lubrication oil supplied to the bearings and a bearing oil pump for supplying the bearings with the lubrication oil have to be large in dimension and capacity, so that the power consumption thereby necessarily becomes large. As a consequence, it has been unable to reduce the quantity of energy consumed from the beginning to the ending of the workpiece grinding.

SUMMARY OF THE INVENTION

It is therefore a primary object of the present invention to provide an improved grinding machine which is capable of reducing the power consumption related to a grinding wheel bearing section including the power for idle rotation at the bearing section, the power for cooling bearing oil, the power for operating a bearing oil pump and the like and hence, of reducing the quantity of energy consumed from the beginning to the ending of a workpiece grinding.

Briefly, according to the present invention, there is provided a grinding machine for grinding with a grinding wheel a workpiece of a predetermined length which is carried to be rotatable together with a work spindle. The grinding machine comprises a wheel spindle for supporting the grinding wheel and fluid bearing means for rotatably supporting the wheel spindle on both sides of the grinding wheel while securing a predetermined rigidity at a grinding point defined between the grinding wheel and the workpiece. The wheel spindle has a diameter determined based on a set value of the quantity of energy consumption, at least at each of portions thereof supported by the fluid bearing means.

With this configuration, the diameter of the wheel spindle and the diameter of the bearing means can be determined in terms of reducing the quantity of energy consumption during the workpiece grinding. By doing so, the power consumption by the grinding machine can be reduced throughout the entire time period of the grinding operation from the beginning to the ending. As a consequence, it can be realized to provide an environment-oriented, energy-saving grinding machine capable of reducing the energy consumption thereby.

BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS

The foregoing and other objects and many of the attendant advantages of the present invention may readily be appreciated as the same becomes better understood by reference to the following detailed description of a preferred embodiment of the present invention when considered in connection with the accompanying drawings, wherein like reference numerals designate the same or corresponding parts throughout several views, and in which:

FIG. 1 is a schematic plan view of a cylindrical grinding machine in an embodiment according to the present invention;

FIG. 2 is a side view of the grinding machine shown in FIG. 1;

FIG. 3 is an enlarged sectional view of a bearing section taken along a horizontal plane of the grinding machine shown in FIG. 1;

FIG. 4(a) is a further enlarged sectional view showing a fluid bearing of the bearing section shown in FIG. 3;

FIG. 4(b) is a cross-sectional view of the fluid bearing shown in FIG. 4(a);

FIGS. 5(a) and 5(b) are a graph and an explanatory view for respectively explaining the relation between the diameter (d) of a wheel spindle 19 and the friction force at a fluid bearing 35 and the relation between the spindle diameter (d) and the power for idle rotation in the fluid bearing 35, wherein FIG. 5(a) shows a bearing characteristic curve while FIG. 5(b) shows various forces acting the wheel spindle 19;

FIG. 6 is a system block diagram of the cylindrical grinding machine including a computer numerical controller;

FIG. 7(a) is a graph with the horizontal axis taken as time axis, showing the power consumption by the cylindrical grinding machine when a workpiece is machined with respective drive circuits shown in FIG. 6 generating powers required for the grinding, wherein a pulse-form line indicated on the lower side represents the power consumption by the grinding machine according to the present invention whereas another pulse-form line indicated on the upper side represents the power consumption by a prior art grinding machine;

FIG. 7(b) is an explanatory view showing the shape and ground areas, as portions to be ground, of a workpiece which is machined in the grinding operation referred to in connection with FIG. 7(a);

FIG. 8(a) is a sectional view of a bearing section taken along a horizontal plane in the prior art cylindrical grinding machine;

FIG. 8(b) is a sectional view of a bearing section taken along a horizontal plane in a cylindrical grinding machine practiced according to the present invention;

FIG. 8(c) is a table showing the diameter of a grinding wheel, the diameter of the wheel spindle and the entire length of the wheel spindle for each of the prior art cylindrical grinding machine and the cylindrical grinding machine practiced according to the present invention;

FIG. 9(a) is a graph with the horizontal axis taken as grinding wheel circumferential speed, showing measured results of idle rotation powers for the grinding wheels in the cylindrical grinding machine practiced according to the present invention and the prior art cylindrical grinding machine;

FIG. 9(b) is a graph showing power consumption related to the wheel spindle bearing section including the power for grinding wheel idle rotation and the powers consumed by a bearing oil supply device and a bearing oil cooler in each of the cylindrical grinding machine practiced according to the present invention and the prior art cylindrical grinding machine;

FIG. 10(a) is a graph showing the relation between the machining time and the power consumption on the basis of values actually measured when a grinding operation is performed in each of the cylindrical grinding machine practiced according to the present invention and the prior art cylindrical grinding machine; and

FIG. 10(b) is an explanatory view of the workpieces used in grinding operations to gather the actually measured values for the graph shown in FIG. 10(a).

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT

(Construction of Grinding Machine)

A grinding machine in an embodiment according to the present invention will be described hereinafter with reference to the accompanying drawings. For the convenience in description, the positional relation regarding the entire construction of the grinding machine will be explained as viewed by an operator standing at the front of the grinding machine (i.e., standing on the left side in FIG. 1). That is, in the following description, when viewed from the operator side, the operator side will be referred to as “front”, the opposite side will be referred to as “rear”, and the right and left sides will be referred to as “right” and “left” respectively. Further, the front-rear direction will be referred as “X-axis direction”, and the left-right direction will be referred to as “Z-direction”.

FIG. 1 is a schematic plan view of a cylindrical grinding machine in the present embodiment, and FIG. 2 is a side view of the cylindrical grinding machine shown in FIG. 1. FIG. 3 is an enlarged sectional view of a bearing section taken along a horizontal plane of the grinding machine shown in FIG. 1. FIG. 4(a) is a further enlarged sectional view showing one of fluid bearings of the bearing section shown in FIG. 3, and FIG. 4(b) is a cross-sectional view of the fluid bearing shown in FIG. 4(a).

The cylindrical grinding machine 10 has all drives controllable by a computer numerical controller (CNC) 100 and is composed of a grinding machine main body and various attachments or auxiliary devices (not shown). Main auxiliary devices comprise a bearing oil supply device for static pressure bearings, a bearing oil cooler, air supply equipments, a coolant supply device, a mist collecting device, and duct devices for connecting these devices to the grinding machine main body.

The cylindrical grinding machine 10 is composed of a bed 11 constituting a base component of the cylindrical grinding machine 10, a pair of Z-axis rails 12 arranged on the top surface of the bed 11 to extend in the Z-axis direction, a Z-axis movable member 13 drivingly movable along the Z-axis rails 12 in the Z-axis direction, a pair of X-axis rails 14 arranged on the top surface of the Z-axis movable member 13 to extend in the X-axis direction, an X-axis movable member 15 drivingly movable along the X-axis rails 14 in the X-axis direction, a wheel head 16 mounted on the X-axis movable member 15 and carrying a grinding wheel (T) to drivingly rotate the same, and a pair of left and right work heads 17 arranged on the top surface of the bed 11 for carrying a workpiece W to rotate the same by a work spindle motor 24.

The Z-axis movable member 13 is constructed to be driven by a linear motor, and between the pair of Z-axis rails 12, a magnet 21 of the linear motor and a coil 22 of the linear motor are respectively arranged on the top surface of the bed 11 and the lower surface of the Z-axis movable member 13. That is, the linear motor is composed of the coil 22 for generating an electric field by being electrified and the magnet 21 for generating a power by the mutual action of the electric field with a magnetic field. The Z-axis movable member 13 is driven by the linear motor to move in the Z-axis direction.

Likewise, the X-axis movable member 15 is constructed to be driven by a linear motor, and between the pair of X-axis rails 14, a magnet (not shown) of a linear motor and a coil 23 (the portion indicated by the hatching in FIG. 1) of the linear motor are respectively arranged on the top surface of the Z-axis movable member 13 and the lower surface of the X-axis movable member 15. The linear motor is composed of the magnet and the coil 23, and the X-axis movable member 15 is driven by the linear motor to move in the X-axis direction.

The X-axis movable member 15 is composed of a base member 25 mounted on the Z-axis movable member 13, a wheel head main body 26 fixedly mounted on the base member 25 and constituting a main component of the wheel head 16, and a wheel spindle unit 27 having a wheel spindle19 and removably attached to the wheel head main body 26. The wheel head main body 26 has a protruding portion 28 protruding forward beyond the front end of the base member 25, and the wheel spindle unit 27 is attached to a front surface of the protruding portion 28. Thus, the grinding wheel T is in the state that it largely protrudes forwardly of the wheel head 16, that is, in the state of overhanging. In a modified form, the base member 25 may be excluded, so that the wheel head main body 26 may be mounted directly on the Z-axis movable member 13. In a further modified form, it may be possible not to provide the wheel spindle 19 on the wheel spindle unit 27 which is constituted as a unit to be removably mounted on the wheel head main body 26, but to provide the wheel spindle 19 on the wheel head main body 26 itself.

The wheel head 16 is provided with the wheel spindle 19 to which the grinding wheel T is secured replaceably, and drivingly rotates the grinding wheel T supported thereon by rotating the wheel spindle 19.

The wheel head main body 26 is provided with rotation drive means 29 for drivingly rotating the wheel spindle 19, and the rotation drive means 29 is composed of a motor with a drivingly rotatable spindle and the like. The motor is constituted by a so-called “built-in motor” whose external housing is formed bodily with the wheel head main body 26. A drive pulley 30 is secured to an end of the spindle of the rotation drive means 29 to be rotatable together with the spindle.

The wheel head main body 26 is provided with a tension pulley 31, which is vertically movable in front (on the left side as viewed in FIG. 2) of the drive pulley 30. The tension pulley 31 is adjustable in its vertical position to make adjustable the tension of a belt 33 wound between the drive pulley 30 and a wheel spindle pulley 32 referred to later.

The wheel spindle unit 27 is composed of a unit base 34 removably attached to the front surface of the protruding portion 28 of the wheel head main body 26, a pair of left and right fluid bearings 35 provided on a front surface of the unit base 34, the wheel spindle 19 supported at opposite ends thereof respectively by the fluid bearings 35 and having the grinding wheel T secured thereto, and a wheel guard 36 for covering the grinding wheel T.

The wheel spindle 19 extends in the Z-axis direction and as shown in FIG. 3, is composed of a first spindle component 38 which is provided at its one end with a flange portion 37 for securing the grinding wheel T thereto, a second spindle component 39 capable of being coupled with one end of the first spindle component 38, and coupling means 40 for making the first spindle component 38 and the second spindle component 39 coupled with, and separated from, each other selectively. That is, the wheel spindle 19 is axially divided into the first and second spindle components 38, 39 at its axial mid portion. Thus, in the coupled state, the wheel spindle 19 takes the construction that it is supported on both sides of the grinding wheel T, and hence, can attain a rigidity which is the same to, or more than, that in the prior art grinding machine even though it is designed to be smaller in its diameter.

The first spindle component 38 is rotatably supported by the bearing 35 at a portion adjacent to the flange portion 37 and is supported by a thrust bearing 41 at its other end. The wheel spindle pulley 32 is secured to the first spindle component 38 between the bearing 35 and the thrust bearing 41. The belt 33 is wound between the wheel spindle pulley 32 and the drive pulley 30 on the side of the wheel head main body 26, so that the drive power from the rotation drive means 29 is transmitted to the wheel spindle 19 to rotate the wheel spindle 19.

The second spindle component 39 is provided with moving means 42 for axially moving the second spindle component 39, at an end opposite to the side on which it is coupled with the first spindle component 38, and is movable axially. The second spindle component 39 is rotatably supported by the bearing 35 arranged between the moving means 42 and the side for coupling with the first spindle component 38. In FIG. 3, a numeral 43 denotes an automatic balancer capable of automatically righting the runout of the grinding wheel T.

The first spindle component 38 and the second spindle component 39 are mutually coupled by the coupling means 40. When the grinding wheel T is to be replaced with new one, the coupling of the first spindle component 38 with the second spindle component 39 by the coupling means 40 is released to move the second spindle component 39 away from the first spindle component 38, whereby a predetermined space is secured between the first spindle component 38 and the second spindle component 39. The space enables the grinding wheel T to be detached from, or to be attached to, the flange portion 37 of the first spindle component 38 by means of bolts (not shown).

The bearings 35 of the wheel spindle unit 27 are constituted by fluid bearings each constructed to operate by utilizing fluid which is supplied through fluid supply passages formed in the wheel spindle unit 27 and the wheel head main body 26. Joints means 44 are provided between the wheel spindle unit 27 and the wheel head main body 26 for making it possible that supply passages provided in each of them can be joined with, or separated from, each other.

As shown in FIG. 4(a) in detail, each of the fluid bearings 35 takes a construction having a bearing member 48 for rotatably supporting the wheel spindle 19, a first supply pocket or portion 49 for supplying bearing oil (i.e., lubrication oil) between the bearing member 48 and the wheel spindle 19, a pair of draining pockets or portions 50 arranged at axially opposite sides of the first supply portion 49 for draining the bearing oil, and a pair of second supply pockets or portions 51 arranged axially outsides of the draining portions 50 for supplying air which is pressurized to a predetermined pressure. Each fluid bearing 35 is provided with end members 52 respectively at opposite ends of the bearing member 48, and a clearance of a predetermined width is formed between each of the end members 52 and a corresponding one of the axial opposite ends of the bearing member 48 to serve as the second supply portions 51.

Each bearing member 48 has its inner diameter which is made to be slightly larger than the diameter of the wheel spindle 19 and is formed with the first supply portion 49 and the draining portions 50 on an internal surface thereof. In each bearing member 48, a clearance (t1) between the wheel spindle 19 and each of internal surface portions which is defined between the first supply portion 49 and each draining section 50 in the axial direction is made to be slightly narrower than another clearance (t2) between the wheel spindle 19 and each of internal surface portions which is defined between each draining section 50 and each second supply portion 51 next thereto.

An internal surface portion 54 of each end member 52 is made to be approximately the same diameter as each internal surface portion 53 b which is defined between each draining portion 50 and each second supply portion 51 in the axial direction. It is to be noted that the supporting accuracy and the like of each fluid bearing 53 is adjustable by properly setting the clearances between these surface portions and the wheel spindle 19.

As shown in FIG. 4(b), each fluid bearing 35 is connected with a unit side supply passage 46 a at the first supply portion 49 in the axial direction and over the wheel spindle 19 in the vertical direction, and is also connected with a unit side draining passage 46 b at each draining portion 50 in the axial direction and under the wheel spindle 19. As shown in FIG. 3, the unit side supply passage 46 a and the unit side draining passage 46 b are connected by the joint means 44 to a body side supply passage 45 a and a body side draining passage 45 b of the wheel head main body 26, respectively. Further, the body side supply passage 45 a and the body side draining passage are connected to a pump and a reservoir of the bearing oil supply device (all not shown).

Thus, the bearing oil reserved in the reservoir of the bearing oil supply device is adjusted by the pump to a predetermined pressure and is supplied to the first supply portion 49 through the body side supply passage 45 a and the unit side supply passage 46 a, while the bearing oil collected at the draining portions 50 are drained through the unit side draining passage 46 b and the body side draining passage 45 b and is cooled by the bearing oil cooler.

Further, as best shown in FIG. 3, the second supply portions 51 are connected to an air supply passage 47, and air of a predetermined pressure supplied from an air supply device (not shown) is supplied to the second supply portions 51 through the air supply passage 47. For the wheel spindle unit 27, a CBN (Cubic Boron Nitride) grinding wheel with a diameter selected in a range of 100 to 200 mm is used, so that it becomes possible to use a smaller diameter grinding wheel than those used conventionally. Although not illustrated in the drawings, the wheel spindle unit 27 and the wheel head main body 26 are secured to each other by connections using bolts or the like or by suitable lock mechanisms or the like.

FIGS. 5(a) and 5(b) are a graph and an explanatory view for explaining the relation between the spindle diameter (d) of the wheel spindle 19 and the friction force of each fluid bearing 35 or the relation between the spindle diameter (d) and the idle rotation power of each fluid bearing 35 in the present invention, wherein FIG. 5(b) shows various forces acting on the wheel spindle 19, whereas FIG. 5(a) represents a bearing characteristic curve.

In FIG. 5(b), symbol “P” denotes a load such as grinding force or the like acting on the wheel spindle 19, symbol “μP” denotes a rotational friction force which is generated through the bearing oil filled in a clearance between the wheel spindle 19 and the internal surface of each bearing member 48 of each fluid bearing 35, symbol “p” a pressure exerted on a bearing projection area (i.e., the area made by the projection of the wheel spindle 19), symbol “η” denotes the viscosity of the bearing oil, symbol “μ” denotes friction coefficient, symbol “L” denotes the length of each fluid bearing 35, symbol “N” denotes the rotational speed of the wheel spindle 19, and symbol “ηN/p” denotes a bearing constant.

FIG. 5(a) represents the bearing characteristic curve, in which three zones including a boundary lubrication zone, a mixed lubrication zone and a fluid lubrication zone are made depending on the range of the bearing constant (ηN/p). Each fluid bearing 35 in the present invention is designed for use in the fluid lubrication zone shown in FIG. 5(a), wherein the friction coefficient (μ) is in proportion to the bearing constant (ηN/p).

Where the circumferential speed and the diameter of the grinding wheel T are represented respectively as “V” and “D”, the circumferential speed (V) is proportional to a product “N·D” and is expressed as “V∝N·D” by the use of symbol “∝” denoting proportion. Further, the pressure (p) exerted on the bearing projection area is expressed as “p=P/(d·L)” because the projection area of each bearing 35 is “d·”. Where symbol (k) is taken to denote the ratio of the length (L) to the spindle diameter (d) in each bearing 35, the pressure (p) is expressed as “p=P/(k·d2), and hence, the rotational friction force (μP) of the wheel spindle 19 can be expressed as follows: μP∝(ηN/p)·P=ηN·k·d2∝η·k·d2V/D  (Expression 1)

And, the rotational friction force (μP) of the wheel spindle 19 is a product of the friction force (μP) multiplied by the radius (d/2) and hence, can be expressed as follows: η·k·d3·V/2D  (Expression 2)

In this expression, the viscosity (η) of the bearing oil depends on the property of a bearing oil to be used. In the present invention, the bearing oil is used as that used in the prior art cylindrical grinding machine, and the viscosity of the bearing oil is about 2 cSt (i.g., centi-stokes).

Further, the ratio (k) of the length (L) to the spindle diameter (d) in each bearing 35 is generally determined in dependence on the purpose of use (e.g., the ration L/d is a value in a range of 2 to 4 or so), and the cylindrical grinding machine according to the present invention was designed to have approximately the same value as used in the prior art grinding machine, that is, to take a value k=1.5. Further, the circumferential speed (V) of the grinding wheel T was designed to 120 m/s (meters per second) which is the same value as used in the prior art grinding machine.

From the foregoing, the power consumption by the grinding wheel T can be considered to exclude the constants in the expression η·k·d3·V/2D and hence, is proportional to d3/D. That is, since the power consumption by the grinding wheel T does not depend on the load such as a grinding force exerted on the wheel spindle 19 and since it is proportional to the cube of the spindle diameter (d) of the bearing component, but is inversely proportional to the diameter (D) of the grinding wheel T, it is understood that the diameter (D) of the bearing prevails over other parameters.

Accordingly, based on results of the foregoing analysis, the diameter (d) of each bearing 35 is determined based on a set value for the quantity of energy consumption in terms of reducing the quantity of energy consumption by reducing the power consumption by the rotation of the grinding wheel T and in particular, the idle rotation power which influences largely upon the quantity of energy consumption from the beginning to the ending of a workpiece grinding as well as by reducing the accompanying power consumption related to the wheel spindle including the power for bearing oil cooling, the power for the bearing pump and so forth. Alternatively, the set value for the quantity of energy consumption is determined based on a reduction target for the quantity of energy consumption during a workpiece grinding in the prior art cylindrical grinding machine, and the diameter (d) of each bearing 35 is determined to satisfy such a reduction target. In this case, in taking into consideration design parameters such as, for example, the ratio (k) of the length (L) to the spindle diameter (d) in each bearing 35, the viscosity (η) of the bearing oil, the diameter (D) of the grinding wheel T, the circumferential speed (V) of the grinding wheel T and the like on the basis of the power consumption by each bearing 35 or the quantity of energy consumption from the beginning to the ending of a workpiece grinding, the diameter (d) of each bearing 35 is determined so that a predetermined rigidity can be secured at the grinding point (i.e., a point where the grinding wheel T contacts the workpiece W).

(Operation of System)

FIG. 6 shows a system including a computer numerical controller according to the present invention. The system including the computer numerical controller according to the present invention is composed of the cylindrical grinding machine 10, the computer numerical controller 100, a drive circuit (DU_Z) 201 for driving the Z-axis movable member 13, a drive circuit (DU_X) 202 for driving the X-axis movable member 15, a drive circuit (DU_T) 203 for driving the rotation drive means 29, a drive circuit (DU_C) 204 for driving the coolant supply device 20 and a drive circuit (DU_S) 205 for driving the work spindle motor 24.

The computer numerical controller 100 executes program controls of the drive circuit (DU_Z) 201, the drive circuit (DU_X) 202, the drive circuit (DU_T) 203, the drive circuit (DU_C) 204 and the drive circuit (DU_S) 205 through an interface 103 in accordance with NC data 102 defining machining data.

The drive circuit (DU_Z) 201 drives the Z-axis movable member 13 in the Z-axis direction by the linear motor composed of the coil 22 and the magnet 21 by electrifying the coil 22 to generate an electric field and by generating a power through the mutual operations of a magnetic field of the magnet 21 with the electric field.

Likewise, the drive circuit (DU_X) 202 drives the X-axis movable member 15 in the X-axis direction by the linear motor composed of the coil 23 and the magnet by electrifying the coil 23 to generate an electric field and by generating a power through mutual operations of a magnetic field of the magnet with the electric field.

The drive circuit (DU_T) 203 rotationally drives the rotation drive means 29 being a built-in motor and rotates the wheel spindle 19 and the grinding wheel T by transmitting the drive power from the drive pulley 30 to the wheel spindle pulley 32 through the belt 33.

The drive circuit (DU_C) 204 drives the coolant supply device 20 to make coolant ejected toward the grinding point.

The drive circuit (DU_S) 205 rotationally drives the work spindle motor 24 at a predetermined rotational speed to drive the workpiece W set on the work heads 17.

FIG. 7(a) is a graph with the horizontal axis taken as time axis, showing the power consumption of the cylindrical grinding machine when a workpiece is machined while the aforementioned respective drive circuits generate powers required for the grinding, wherein a pulse-form line indicated on the lower side represents the power consumption by the grinding machine according to the present invention whereas another pulse-form line indicated on the upper side represents the power consumption by the prior art grinding machine. Further, FIG. 7(b) is an explanatory view showing the shape and ground areas, as portions to be ground, of a workpiece W which is machined in the grinding operation referred to in connection with FIG. 7(a). Where the ground areas of the workpiece W are determined as three portions marked A, B and C as shown in the drawing, the pattern of the power consumption in grinding these three portions is indicated in FIG. 7(a) to correspond respectively to periods or segments marked A′, B′ and C′ in the grinding machine according to the present invention and to periods or segments marked A″, B″ and C″ in the prior art grinding machine.

Next, detailed description with reference to FIG. 7(a) will be made regarding the power consumption which depends on the power consumptions by the respective drive circuits in grinding the workpiece W shown in FIG. 7(b) by each of the grinding machine according to the present invention and the prior art grinding machine. First of all, the pattern of power consumption will be described in the case that the grinding operation is performed by the grinding machine according to the present invention.

The time when all the preparations required for the machining of the workpiece W have been completed with the same being set on the work heads 17 is set as machining time “0” on the horizontal axis and as power consumption “0” on the vertical axis. By the time “s1”, the work spindle motor 27 is driven by the drive circuit (DU_S) 205 to rotate the workpiece W at the predetermined rotational speed and the grinding wheel T is driven by the drive circuit (DU_T) 203. The power consumption at this time is indicated as “L1” inclusive of those consumptions by the bearing oil supply device and the bearing oil cooler. Then, by the time “s2”, the coolant supply device 20 is driven by the drive circuit (DU_C) 204 to make the coolant ejected toward the grinding point. The power consumption at this time is indicated as “L2”.

Thereafter, by the time “s3”, the drive circuit (DU_Z) 201 electrifies the coil 22 to drive the Z-axis movable member 13 by the linear motor in the Z-axis direction. Further, the drive circuit (DU_X) 202 electrifies the coil 23 to drive the X-axis movable member 15 by the linear motor in the X-axis direction. The time period from “s2” to “s3” is the time period for positioning the grinding point by the linear motors in the Z-axis direction and the X-axis direction. These positioning operations are performed to move the grinding wheel T between the ground areas and are called as “index operations”. The power consumption at this time is indicated as “L5”. Although in the pattern of power consumption shown in FIG. 7(a), the power consumption “L5” during the index operation in the Z-axis direction is made larger than the power consumption “L4” during the index operation in the X-axis direction, they may be reverse in the relation of their magnitudes. In addition, the index operations in the Z-axis direction and the X-axis direction may be performed simultaneously at least in a part of the sections. The present invention features that the power consumption during the index operation is larger than the power consumption “L3” during a grinding period referred to later. This means that it is suffice that the power consumption during the index operation at least in the Z-axis direction or the X-axis direction is larger than the power consumption “L3” during the grinding period.

Subsequently, the time period from “s3” to “s4” is the time period in which the grinding wheel T on the X-axis and Z-axis movable members 15, 13 having been positioned by the aforementioned index operations enters into a grinding stage while gradually increasing the infeed amount from a position adjacent to the grinding point, and this infeed of the grinding wheel T is called as an “approach stage”. The power consumption at this stage is the same as that in the time period from “s1” to “s2”.

The time period for the grinding stage begins upon completion of the approach stage and ends at the time “s5”. The power consumption at this grinding stage increases from “L2” to “L3” with the increase of the load by grinding. Then, until the time “s6”, that is, during the time period from the termination of the infeed of the grinding wheel T to the extinction of sparks, the grinding wheel T is caused to remain as it is in the X-axis direction for a spark-out grinding.

The aforementioned time period from “s2” to “s6” is the machining segment A′ corresponding to the ground area A of the workpiece W, and in this machining example, the same machining as aforementioned is performed in turn in the machining segments marked B′ and C′, whereby the grinding operation is terminated at the time period “s7”. Thereafter, by the time “s8”, the operation of the coolant supply device 20 by the drive circuit (DU_C) 204 is discontinued to let the power consumption go down to “L1”. Further, by the time “s9”, the Z-axis movable member 13 and the X-axis movable member 15 are returned to a predetermined original position by being driven by the drive circuit (DU_Z) 201 and the drive circuit (DU_X) 202 respectively in the Z-axis direction and the X-axis direction.

Since at this time, the grinding of the workpiece W is terminated, the work spindle motor 24 is stopped by the drive circuit (DU_S) 205 to discontinue the rotation of the workpiece W, and the rotation of the grinding wheel T is discontinued by the drive circuit (DU_T) 203. Further, the operations of the bearing oil supply device and the bearing oil cooler are also stopped to complete the grinding operation, whereby the power consumption is returned to “0”.

Next, description will be made regarding the grinding performed by the prior art grinding machine, wherein the operations overlapping those described above will be described simply.

Upon completion of the machining preparations, by the time “s1”, the workpiece W is rotated at the predetermined rotational speed and the grinding wheel T is rotated in the same manner as that described with respect to the present invention. The power consumption at this time is indicated as “M1”, which is larger than the power consumption “L1” in the present invention. This is because in the prior art grinding machine, the diameters of the grinding wheel T and the wheel spindle 19 are larger, which requires an in crease in the power consumption. Then, by the time “s2”, coolant is ejected toward the grinding point. The power consumption at this time is indicated as “M2”.

Next, description will be made regarding the machining segment A″ corresponding to the ground area A of the workpiece W. With respect to the approach time period (s3 to s4), the grinding time period (s4 to s5) and the spark-out grinding time (s5 to s6) as explained in the foregoing machining example in the present invention, the same is applied to the prior art grinding machine, and respective power consumptions during these time periods are indicated as “M2”, “M5” and “M2”, respectively. The same machining as that in the machining segment A″ is performed in each of machining segments B″ and C″, and after the operation of the coolant supply device is stopped, the grinding wheel T is returned to an original position, whereby the grinding operation is completed at the time “s10”.

In the grinding machine according to the present invention, the power consumption by the idle rotation of the grinding wheel T and by the bearing oil supply device and the bearing oil cooler which are required to be operated in connection therewith is at the level “L1” indicated in FIG. 7(a), and the power at this level is required throughout the entire time period (0 to s9) from the beginning to the ending of the workpiece grinding operation.

Effects of the Embodiment

As described above, in the present embodiment, the power consumption by the bearing section 27 or the quantity of energy consumption from the beginning to the ending of a workpiece grinding operation is set to a predetermined quantity, in dependence on which the diameter of each bearing 35 is determined so that a predetermined rigidity can be secured at the grinding point. Consequently, as shown in FIG. 7(a), the power consumption at the level “M1” by the prior art grinding machine is lowered to that at the level “L1” by the cylindrical grinding machine in the present embodiment, so that the power consumption or the quantity of energy consumption can be reduced throughout the entire time period (0 to s9) from the beginning to the ending of the workpiece grinding operation. The quantity of energy consumption which can be reduced in the present embodiment can be indicated as that covered by the hatched area in FIG. 7(a). Accordingly, it can be realized in the present embodiment to provide the environment-oriented, energy-saving grinding machine capable of reducing the quantity of energy consumption.

Example practiced

FIG. 8(a) is a sectional view of a bearing section taken along a horizontal plane in the prior art cylindrical grinding machine, FIG. 8(b) is a sectional view of a bearing section taken along a horizontal plane in a cylindrical grinding machine practiced according to the present invention, and FIG. 8(c) is a table showing the diameter of the grinding wheel T, the diameter of the wheel spindle 19 and the entire length of the wheel spindle 10 in each of the respective grinding machines. In the practiced example, the power consumption related to the grinding wheel bearing was determined with the aim of lowering the idle rotation power for the grinding wheel T, and the diameter of the wheel spindle 19 was designed so that a predetermined rigidity of 100 N/μm (newtons per micrometer) was able to be secured as that at the grinding point of the grinding wheel T.

FIG. 9(a) is a graph with grinding wheel circumferential speed on the horizontal axis, showing measured results of idle rotation power for the grinding wheel in each of the cylindrical grinding machine according to the present invention and the prior art cylindrical grinding machine. FIG. 9(b) is a graph showing the power consumption related to the wheel spindle bearing including the power for grinding wheel idle rotation and the powers consumed by the bearing oil supply device and the bearing oil cooler in each of the cylindrical grinding machine practiced according to the present invention and the prior art cylindrical grinding machine.

As demonstrated in FIG. 9(a), the idle rotation power for the grinding wheel T in the cylindrical grinding machine practiced according to the present invention was about one fourth (¼) of that in the prior art cylindrical grinding machine. In the case that the circumferential speed of the grinding wheel T was set to 120 m/s (meters per second) which has been wide use in terms of machining efficiency, the idle rotation power in the cylindrical grinding machine practiced according to the present invention was 1 kW. Further, as demonstrated in FIG. 9(b), with the decrease of the idle rotation power for the grinding wheel T, the power consumption related to the grinding wheel bearing including the powers consumed by the bearing oil supply device and the bearing oil cooler was also reduced at a similar rate and was able to be greatly reduced to 2.3 kW in the cylindrical grinding machine practiced according to the present invention thought that in the prior art cylindrical grinding machine was 9 kW.

FIG. 10(a) is a graph showing the relation between the machining time and the power consumption on the basis of the values which were actually measured values when a workpiece W shown in FIG. 10(b) was ground in each of the cylindrical grinding machine practiced according to the present invention and the prior art cylindrical grinding machine. The workpiece W was a stepped shaft with five stepped portions and had five ground areas. The total machining time in the cylindrical grinding machine practiced according to the present invention was reduced by the high speed driving using the linear motors to 44 seconds which was 12% shorter than 50 seconds taken by the grinding in the prior art cylindrical grinding machine. Further, in the cylindrical grinding machine wherein the diameter of the fluid bearings 35 for the grinding wheel T was designed on the basis of the quantity of power consumption by the bearing section 27 or the energy consumption from the beginning to the ending of the workpiece grinding operation, the power consumption related to the grinding wheel bearing including the idle rotation power for the grinding wheel T and the powers consumed by the bearing oil supply device and the bearing oil cooler was able to be reduced by about 7 kW at all the time points from the beginning to the ending of the workpiece grinding operation, in comparison with that in the prior art cylindrical grinding machine. The reduction of about 7 kW in the power consumption corresponds to the reduction of about 0.1 kWh per workpiece when converted into the quantity of energy consumption.

Obviously, numerous modifications and variations of the present invention are possible in light of the above teachings. It is therefore to be understood that within the scope of the appended claims, the present invention may be practiced otherwise than as specifically described herein. 

1. A grinding machine for grinding with a grinding wheel a workpiece of a predetermined length which is carried to be rotatable together with a work spindle, the grinding machine comprising: a wheel spindle for supporting the grinding wheel; and fluid bearing means rotatably supporting the wheel spindle on both sides of the grinding wheel while securing a predetermined rigidity at a grinding point defined between the grinding wheel and the workpiece; wherein the wheel spindle has a diameter determined based on a set value for the quantity of energy consumption, at least at portions thereof supported by the fluid bearing means.
 2. The grinding machine as set forth in claim 1, wherein the wheel spindle has the diameter determined based on the set value for the quantity of energy consumption which value is determined based on a power consumption by the rotation of the grinding wheel.
 3. The grinding machine as set forth in claim 1, wherein the wheel spindle is divided at its axial mid portion into first and second spindle components, the grinding machine further comprising; coupling means provided between the first and second spindle components for separating or coupling the first and second spindle components at an axial position where the grinding wheel is supported on the wheel spindle.
 4. A grinding machine for grinding with a grinding wheel a workpiece of a predetermined length which is carried to be rotatable together with a work spindle, the grinding machine comprising: a wheel spindle for supporting the grinding wheel at an axial mid portion thereof and composed of first and second spindle components divided at the axial mid portion; coupling means provided between the first and second spindle components for separating or coupling the first and second spindle components at an axial position where the grinding wheel is supported on the wheel spindle; and a pair of fluid bearings for rotatably supporting respective ends, on the sides opposite to the axial mid portion, of the first and second spindle components while securing a predetermined rigidity at a grinding point defined between the grinding wheel and the workpiece; wherein each of the first and second spindle components has a diameter determined based on a set value for the quantity of energy consumption, at least at a portion thereof supported by a corresponding one of the fluid bearings.
 5. The grinding machine as set forth in claim 4, wherein the diameter of the first and second spindle components is determined based on the set value for the quantity of energy consumption which value is determined based on a power consumption by the rotation of the first and second spindle components. 